Appendix II. £09 the boiler; but it is dirty, and the stokehold temperature is as high as n6d F. The closed ashpit is shewn by the Howden system, Fig. 871, where the air is forced in at A by a fan, and passing over tubes B B that are heated by hot gases from the boiler, enters the fire through the fire-door c, both above and below the firebars. The results are more economical than in the last system, but the temperature of the stokehold is still high. In the third method, shewn by the Meldrum furnace, Fig. 8710, air is introduced at the blowers B, by means of a jet of steam from the pipe A, and the ashpit is closed, but the ordinary firing arrangements are not interfered with. The system is especially suitable for dust fuels. Induced draught has many advocates. It is effected by a fan in the uptake, which removes air from the boiler tubes and causes, a partial v^fcuum into which the combustion air enters by passing over the fire, Its best representative is the Ellis and Eaves system, Fig. 872. The air enters by tubes A, where it is heated by furnace gases, and then through the ashpit door as before. Upon reaching the uptake it is deflected through the suction fan B, or may ascend directly to the chimney if damper c be opened and D closed. Its efficiency is greatly increased by the Serve tubes shewn, and retarding plates, and the stokehold is both clean and cool. There is said to be decreased injury to boiler tubes through the air entering at their centres instead of impinging on their edges, and an evaporation of 60 Ibs. per sq. ft. of grate is easily obtained.